Liquid-sealing type variation isolating apparatus

ABSTRACT

The liquid-sealing type vibration isolating apparatus of the present invention includes a coupler attached to a vibrating body, a holder, an insulator for absorbing and isolating vibration from the vibrating body at a position between the coupler and the holder, and a vibration isolating mechanism directly following the insulator and including liquid chambers sealing an incompressible fluid. This vibration isolating mechanism has a main chamber sealing a liquid, having a part of wall thereof formed by the insulator, an auxiliary chamber communicating with the main chamber via an orifice, and an equilibrium chamber provided in a portion of the main chamber via a diaphragm and having a varying volume in the chamber. The vibration isolating apparatus further includes switching means for introducing a negative pressure and the atmospheric pressure continuously or in synchronization with vibration of the vibrating body, and control means for controlling this switching operation.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a liquid-sealing type vibrationisolating apparatus which gives a vibration isolating effect on thebasis of the flowing action of a fluid (liquid) sealed therein. Moreparticularly, the present invention relates to a liquid-sealing typevibration isolating apparatus in which the liquid in a liquid chamber isvibrated at a certain frequency, the vibrating apparatus thereof havinga simple structure, and isolation of vibration of a plurality of kindsis effectively accomplished over a wide scope ranging from low to highfrequency regions.

[0003] 2. Description of the Related Art

[0004] A vibration isolating apparatus, particularly an automotiveengine mount must be capable of coping with a wide range of frequenciesbecause the engine serving as a power source is used under variousconditions ranging from idling operation to the maximum velocity ofrevolutions. For this purpose, there has already been invented anapparatus known as a liquid-sealing type engine mount (vibrationisolating apparatus) in which two liquid chamber are provided and areconnected with an orifice, such as the one disclosed in JapaneseUnexamined Patent Publication

[0005] The aforesaid known apparatus is designed to have two orifices tocope with two kinds of input frequency within the low-frequency region.The apparatus can cope (vibration isolation) with two kinds of vibrationsuch as engine idling vibration and engine shaking by operating thesetwo orifices. These kinds of vibration have however a frequency with arange of from 10 to 30 Hz. An automobile engine is used under diverseand various circumstances, and the range of frequencies of vibration andnoise propagating through the engine and the engine mount supporting theengine covers a wide region. Recently, in particular, vibration andnoise associated with engine noise including a dull sound which is avibration within the higher frequency region, in addition to theforegoing idling vibration and engine shake are forming an issue.

[0006] More recently, tuning of an engine mount is becoming more commonwith a view to isolating a dull sound associated with vibration of arelatively high frequency within a range of from 100 to 600 Hz. For thepurpose of coping with a plurality of conditions as described above,there has already been known a liquid-sealing type vibration isolatingapparatus having a liquid chamber and a fluid bag to change the volumeat a specific frequency within the fluid bag, as disclosed, for example,in Japanese Patent Publication No. 6-29634.

[0007] In this known apparatus, the fluid bag is provided in the liquidchamber to change the volume thereof at a prescribed frequency, therebycausing a liquid in the liquid chamber on the vibration input side toflow via an orifice toward another side liquid chamber. Morespecifically, in the low-frequency region mainly comprising idlingvibration, the liquid pressure in the liquid chamber on the vibrationinput side is increased so as to obtain a high damping property. In thehigh-frequency region, on the other hand, increase in the liquidpressure in the liquid chamber on the vibration input side is avoided toobtain a low dynamic spring constant. For recent automotive enginemounts, however, a vibration isolating apparatus should cover idlingvibration against which resonance phenomenon should be avoided byreducing the dynamic constant as vibration within the low-frequencyregion, and vibration associated with engine shaking against whichvibration should be inhibited by increasing the damping property.

[0008] Further, in this known apparatus, a fluid pressure generatingdevice is need for causing the volume thereof to be changed, so thatthere are raised the following problems.

[0009] (1) An additional space has to be secured in an engine room.

[0010] (2) The apparatus itself increases a production cost.

[0011] In order to achieve a vibration isolating apparatus capable ofcoping with these contradictory conditions, simple vibrating of theliquid in the liquid chamber on the vibration input side in the same orreversed phase is insufficient.

[0012] To cope with these multiple conditions, furthermore, there isalready known an apparatus called a voice-coil type liquid-sealing typevibration isolating apparatus in which a liquid chamber is provided andwhich has a vibrator comprising a voice coil or the like vibrating at acertain frequency in the liquid chamber, as disclosed, for example, inJapanese Unexamined Patent Publication No. 5-149369. An apparatus ofthis type has however inevitably a complicated structure because of thenecessity of a plurality of liquid chambers, a movable piece comprisinga piston or the like in the liquid chamber and a voice coil for drivingsuch a movable piece. The vibration isolating apparatus as a wholebecomes unavoidably heavier because of shaking coils, permanent magnetsand many other parts.

SUMMARY OF THE INVENTION

[0013] The present invention was developed to solve the problems asdescribed above, and has an object to provide a vibration isolatingapparatus capable of certainly inhibiting vibration occurring from avibrating body from propagating in the vehicle room.

[0014] Another object of the present invention is to provide aliquid-sealing type vibration isolating apparatus permitting giving alow dynamic spring constant even in the high frequency region for thepurpose of isolating vibration in a relatively high frequency region.

[0015] Further another object of the present invention is to provide aliquid-sealing type vibration isolating apparatus which can give a lowdynamic spring constant (low dynamic spring property) for both vibrationin a low-frequency region mainly comprising idling vibration andvibration in a high-frequency region causing a dull sound, and give ahigh damping property against vibration in a low-frequency region comingfrom engine shake.

[0016] To achieve these objects, according to the present invention, aliquid-sealing type vibration isolating apparatus is provided whichcomprises a coupler attached to a vibrating body, a holder attached tothe vehicle body side, an insulator which is provided between thecoupler and the holder and absorbs and isolates vibration from thevibrating body, and a vibration isolating mechanism which directlyfollows the insulator and is formed with a liquid chamber sealing aliquid which is an incompressible fluid; the vibration isolatingmechanism comprising a main chamber having a wall thereof formed by apart of the insulator and sealing the liquid, an auxiliary chamberconnected to the main chamber so that the liquid flows through anorifice, an equilibrium chamber which is provided at a part of the mainchamber via a diaphragm and is formed so that the volume thereof in thechamber changes, and an air chamber which surrounds the auxiliarychamber via another diaphragm and constantly receives air; wherein thereare further provided switching means which conducts a switchingoperation so as to alternately introduce any one of a negative pressureand the atmospheric pressure into the equilibrium chamber having theaforesaid construction constantly or in synchronization with enginevibration, and in addition, control means which controls the switchingoperation of the switching means.

[0017] By adopting the constitution as described above, the followingeffects are available in the present invention. In the presentinvention, more specifically, an equilibrium chamber is provided via adiaphragm in the main chamber, and a negative pressure or theatmospheric pressure is appropriately introduced into the equilibriumchamber. Introduction of the negative pressure or the atmosphericpressure is accomplished through switching means under control by thecontrol means. That is, operation of this switching means causes thenegative pressure to be periodically introduced at a certain frequencyor causes a certain negative pressure to be continuously introduced. Asrequired, the equilibrium chamber is kept in a state open to the openair. Therefore, in response to idling vibration of the engine forming avibrating body, the pressure (volume) of the equilibrium chamber isaltered through an ON/OFF operation of the switching means, therebyabsorbing fluctuations of the liquid pressure in the main chamber causedby idling vibration entered via the insulator. This results in a reduceddynamic spring constant of the spring system formed by the insulator andthe vibration isolating mechanism. Idling vibration is thus absorbed andisolated.

[0018] To cope with high-frequency vibration within a range of from 100to 600 Hz causing a dull sound, which is a problem during travel of avehicle, the switching means is operated to bring the equilibriumchamber into a state open to the open air. As a result, the volume inthe equilibrium chamber freely changes relative to high-frequencyvibration entered via the insulator and the liquid in the liquidchamber. This permits free vibration of the insulator and the liquid inthe liquid chamber, whereby the dynamic spring constant of the springsystem formed by the vibration isolating mechanism is inhibited to a lowlevel. An improved isolating effect is thus available againsthigh-frequency vibration. In the present invention, as described above,the switching means comprising a switching valve or the like, theorifice and the equilibrium chamber permit absorption and isolation ofmultiple kinds of vibration.

[0019] The liquid is allowed to flow through an orifice connecting themain chamber and the auxiliary chamber to isolate engine shake which isvibration of a frequency further lower than idling vibration, therebyabsorbing and isolating the engine shake. More specifically, sincevibration associated with engine shake has a frequency of about 10 Hz,it is difficult to isolate vibration by reducing the dynamic springconstant. In the present invention, therefore, a certain negativepressure is introduced into the equilibrium chamber forming thevibration isolating mechanism so as to bring the volume of theequilibrium chamber to null. This allows the liquid to flow through anorifice formed between the main chamber and the auxiliary chamber, andviscous drag resulting from the liquid causes production of a prescribeddamping force. This damping force leads to damping of engine shake.

[0020] In another means for achieving the foregoing objects, a vibrationisolating mechanism comprising a liquid chamber and the like is providedin series with the insulator. More particularly, there is provided aliquid-sealing type vibration isolating apparatus, wherein the vibrationisolating mechanism comprises a main chamber which comprises a liquidchamber arranged in series with the insulator and having a wall thereofformed by a part of the insulator, an auxiliary chamber connected to themain chamber so as to allow the liquid to flow via an orifice to themain chamber and separated by a partition plate comprising a rigid bodyfrom the main chamber, an equilibrium chamber formed via a diaphragmbetween the main chamber and the partition plate and arranged so as tointroduce any one of the atmospheric pressure and a negative pressure,and an air chamber provided under the auxiliary chamber via anotherdiaphragm and constantly fed with air. By adopting this configuration,in the present invention, vibration from the vibrating body istransmitted directly to the insulator and the liquid in the mainchamber, thus further improving the vibration isolating effect, inaddition to the foregoing means. A vibration isolating apparatus havingan equilibrium chamber in the main chamber is formed on the basis of theconventional upright-type liquid-sealing type vibration isolatingapparatus, thus permitting improvement of assembly merit of thevibration isolating apparatus as a whole.

[0021] The aforesaid objects are achieved according to the presentinvention also by the vibration isolating apparatus, wherein the lengthL1 of a duct line from the atmospheric pressure inlet to the equilibriumchamber is set at a value determined by the following formula:

0.85 cT/4≦L1≦1.15 cT/4

[0022] where c is the sound velocity (340 m/sec) and T is a period oftime (in seconds) during which the open air is introduced into theequilibrium chamber by the switching means.

[0023] The foregoing objects are achieved, according to the presentinvention, in the vibration isolating apparatus of the above-mentionedconfiguration, by providing an expansion chamber having a largerdiameter than that of the duct line between the atmospheric pressureinlet and the switching means and setting the length L2 between theexpansion chamber and the equilibrium chamber at a value determined bythe following formula:

0.85 cT/4≦L2≦1.15 cT/4

[0024] where c is the sound velocity (340 m/sec) and T is a period oftime (in seconds) during which the open air is introduced into theequilibrium chamber by the switching means.

[0025] According to the vibration isolating apparatus of the presentinvention, furthermore, the coupler attached to the vibrating body andthe insulator provided between the coupler and the holder attached tothe vehicle body side absorb most of vibration transmitted from thevibrating body. The vibration isolating mechanism following directly theinsulator further controls and absorbs vibration. In other words, theliquid sealed in the main liquid chamber and the auxiliary liquidchamber flows through the orifice under the effect of vibration, andthis flow controls and absorbs vibration. At the same time, a negativepressure introduced from the negative pressure source and theatmospheric pressure introduced from the atmospheric pressure inlet arealternately introduced into the equilibrium chamber provided in aportion of the main liquid chamber via a diaphragm. This introduction isaccomplished by a switching operation of the switching means undercontrol by the control means at a frequency f required for synchronizingwith vibration of the aforesaid vibrating body. This alternateintroduction permits alternate introduction of the negative pressure andthe atmospheric pressure at a frequency corresponding to the requiredfrequency, and in response to this, the pressure in the equilibriumchamber, and hence the volume thereof change. This change in volumepositively controls and absorbs changes in the liquid pressure in themain liquid chamber produced by vibration of the vibrating body andentered via the insulator.

[0026] Because the switching means is switched over by switching, thisswitching may cause generation of a harmonic component. In the presentinvention, however, the length L1 of the duct line from the atmosphericpressure inlet to the equilibrium chamber is set at a value determinedby the following formula:

0.85 cT/4≦L1≦1.15 cT/4

[0027] where c is the sound velocity (340 m/sec) and T is a period oftime (in seconds) during which the open air is introduced into theequilibrium chamber by the switching means. A pulse may therefore beproduced in the air introduced from the atmospheric pressure inlet,resulting in a temporary inertial supercharging. A pressure higher thanthe atmospheric pressure would thus be introduced into the equilibriumchamber. In parallel with this, the pressure waveform is corrected, thusresulting in elimination of the unnecessary harmonic component.Fluctuations of pressure in the equilibrium chamber therefore changeinto smooth behavior like a sine wave, hence permitting control offluctuations of liquid pressure in the main liquid chamber in responseto vibration of the vibrating body.

[0028] This is particularly effective when the length L1 of the ductline from the open air inlet to the equilibrium chamber cannot be setwithin the foregoing range. According to the present invention, anexpansion chamber having a diameter larger than that of the duct line isprovided between the open air inlet and the switching means and thelength L2 of the duct line from the expansion chamber to the equilibriumchamber is set at a value determined by the following formula:

0.85 cT/4≦L2≦1.15 cT/4

[0029] where c is the sound velocity (340 m/sec) and T is a period oftime (in seconds) during which the open air is introduced into theequilibrium chamber by the switching means. By only appropriatelyadjusting the length L2 of the duct line from the expansion chamber tothe equilibrium chamber, therefore, the effect substantially the same asabove is available. Therefore, when the length L1 of the duct line fromthe open air inlet to the equilibrium chamber cannot be set within theabove range because of a particular necessity in piping, it suffices toprovide an expansion chamber having a length L2 satisfying the aboveformula.

[0030] In addition, in the vibration isolating apparatus of the presentinvention, the required frequency is the one required for synchronizingwith an idling vibration of the engine.

[0031] Further, the liquid-sealing type vibration isolating apparatusfor achieving another object of the present invention comprises a mainchamber having a wall thereof formed by a part of the insulator andreceiving vibration directly propagating from the insulator, anauxiliary chamber connected to the main chamber via a small-diameterorifice so as to allow the liquid to flow and separated by a firstpartition plate comprising a rigid body from the main chamber, and anequilibrium chamber formed via a diaphragm between the main chamber andthe first partition plate and receiving any one of a negative pressureand the atmospheric pressure; and the liquid-sealing type vibrationisolating apparatus further comprising a second partition plate servingalso as a stopper, provided in the main chamber above the diaphragmforming the equilibrium chamber, a second orifice comprising alarge-diameter orifice in a portion of the second partition plate,switching means for performing a switching operation so as toalternately introduce any one of the negative pressure and theatmospheric pressure into the equilibrium chamber, in synchronizationwith engine vibration, and control means for controlling the switchingoperation of the switching means.

[0032] This constitution provides the following functions. First, as toidling vibration, the negative pressure and the atmospheric pressure arealternately introduced at a specific frequency into the equilibriumchamber provided under the main chamber by operating the switchingmeans. That is, the pressure (volume) in the equilibrium chamber isaltered by ON/OFF-operating the switching means, thereby absorbingfluctuations of liquid pressure in the main chamber caused by idlingvibration entered via the insulator. This reduces the dynamic springconstant of the spring system formed by the insulator and the vibrationisolating mechanism. This permits absorption and isolation of idlingvibration.

[0033] As to engine shake which is vibration of a frequency furtherlower than that of idling vibration, the liquid is caused to flowthrough the small-diameter orifice connecting the main chamber and theauxiliary chamber, thereby absorbing and isolating engine shake. Morespecifically, because engine shake vibration has a frequency of about 10Hz, it is difficult to isolate vibration by reducing the dynamic springconstant. In the present invention, therefore, the volume of theequilibrium chamber is kept null by continuously introducing a certainnegative pressure into the equilibrium chamber forming the vibrationisolating mechanism. This allows the liquid to flow through thesmall-diameter orifice formed between the main chamber and the auxiliarychamber, thereby causing generation of a prescribed damping force underthe effect of viscous drag resulting from the flow of the liquid. Engineshake is thus damped by the action of this damping force.

[0034] On the other hand, with respect to the vibration of a highfrequency of about 100 to 600 Hz which causes a dull sound during travelof a vehicle, the switching means is operated to bring the equilibriumchamber into the state open to the open air. The volume in the chambercan thus freely change in response to vibration of a frequency enteredvia the insulator and the liquid in the main chamber. The liquid in themain chamber is allowed to freely flow through the large-diameterorifice (second orifice) of the second partition plate provided in themain chamber, thus reducing the dynamic spring constant of the springsystem formed by the vibration isolating mechanism to a low level. Theisolating effect against vibration in the high-frequency region is thusimproved. In the present invention, as described above, multiple kindsof vibration can be absorbed and isolated under the effect of theequilibrium chamber capable of changing the inner volume thereof byoperating the switching means comprising a switching valve or the like.

[0035] In the present invention, the second partition plate comprising arigid body is provided above the diaphragm forming the equilibriumchamber in the main chamber. When vibration entered from the vibratingbody has a large amplitude, the downward stroke of the upper couplingmember caused by this vibration from the vibrating body is arrested atthis second partition plate. In other words, the second partition plateserves as an inner stopper of this vibration isolating apparatus. Underthe effect of this stopper function, the diaphragm forming theequilibrium chamber is protected upon input of vibration. As a result,the change in volume of the equilibrium chamber is kept normal, thuspermitting reduction of the dynamic spring constant.

[0036] In the liquid-sealing type vibration isolating apparatus forachieving further another object of the present invention, the vibrationisolating mechanism comprises a liquid chamber sealing an incompressiblefluid, an equilibrium chamber receiving a negative pressure or theatmospheric pressure, and an elastic diaphragm partitioning the liquidchamber and the equilibrium chamber; a plurality of said vibrationisolating mechanisms are provided; a first liquid chamber provided in afirst liquid chamber provided in a first vibration isolating mechanismfrom among these plurality of vibration isolating mechanisms and asecond liquid chamber provided in a second vibration isolating mechanismare connected with a large-diameter orifice; the first liquid chamberprovided in the first vibration isolating mechanism and a third liquidchamber provided in a third vibration isolating mechanism are connectedwith a small-diameter orifice; any one of a negative pressure and theatmospheric pressure is continuously introduced into a first equilibriumchamber provided in the first vibration isolating mechanism viaswitching means alternately in synchronization with engine vibration;and any one of a negative pressure and the atmospheric pressure iscontinuously introduced into a second equilibrium chamber provided inthe second vibration isolating mechanism in compliance with a switchingoperation of the switching means in response to the traveling state ofthe vehicle.

[0037] By adopting the foregoing constitution, the following effects areavailable in the present invention. Vibration from the vibrating body istransmitted via the coupling member to the insulator made of a rubbermaterial or the like. The insulator vibrates or deforms as a result andabsorbs or isolates most of the entered vibration. While most of thevibration is thus isolated at the insulator, a part thereof is notisolated at the insulator, but is isolated at the vibration isolatingmechanism following the insulator. Now, detailed operations of theindividual vibration isolating mechanisms will be described below.First, the vibration isolating function against engine idling vibrationwill be described. In this case, the frequencies to be covered rangefrom about 20 to 40 Hz. A negative pressure is therefore introducedthrough the switching means into the second equilibrium chamber in FIG.1 to bring the volume of the second equilibrium chamber to null. Thatis, the diaphragm in the second vibration isolating mechanism is keptinoperable. In this state, a negative pressure and the atmosphericpressure are alternately introduced into the first equilibrium chamberof the first vibration isolating mechanism at a certain cycle(frequency). As a result, the liquid in the first liquid chamberprovided under the insulator is about to flow through the small-diameterorifice to the third liquid chamber. However, because the negativepressure or the atmospheric pressure is introduced into the firstequilibrium chamber so that the diaphragm is applied with vibration at afrequency higher than the liquid resonance frequency of the liquidpresent in the orifice, the liquid in the first liquid chamber does notflow toward the small-diameter orifice. The status of the liquidpressure in the first liquid chamber largely fluctuates, and the liquidin the first liquid chamber is vibrated in the same phase as the enteredvibration. This inhibits increase in the dynamic spring constant in thepresent vibration isolating apparatus. That is, reduction of the dynamicspring constant is successfully achieved.

[0038] As to engine shake which is vibration caused during travel of avehicle and has a frequency further lower than the idling vibration, anegative pressure is introduced into the first equilibrium chamber tobring the volume of the first equilibrium chamber to null. In otherwords, the diaphragm of the first vibration isolating mechanism is keptinoperable. In this state, when vibration is transmitted from avibrating body such as an engine to the upper coupling member, theliquid pressure in the first liquid chamber increases, and the liquid inthe first liquid chamber flows through the large-diameter orifice to thesecond liquid chamber of the second vibration isolating mechanism. Theflow of the liquid in the first liquid chamber through thelarge-diameter orifice makes it available a high damping property. As aresult, vibration of engine shake having a frequency of about 10 Hz isinhibited. Vibration caused upon engine cranking, or vibration of alarge amplitude caused upon sudden start or sudden acceleration, whichis vibration of a large amplitude at a further lower frequency isinhibited under the effect of the small-diameter orifice. Thesmall-diameter orifice causes the liquid in the first liquid chamber toflow to the third liquid chamber against input of an initial load causedupon installation on the vibrating body, to keep balance of innerpressure in the individual liquid chambers.

[0039] As to vibration within a high frequency region of from 100 to 600Hz, which poses the problem of a dull sound in the vehicle room, theatmospheric pressure is introduced into the first equilibrium chamber ofthe first vibration isolating mechanism to bring the first equilibriumchamber into the state open to the open air. At the same time, anegative pressure is continuously introduced into the second equilibriumchamber forming the second vibration isolating mechanism to bring thevolume of the second equilibrium chamber to null. The vibrationtransmitted through the upper coupling member into the first liquidchamber consequently vibrates the liquid in the first liquid chamber.However, since the first equilibrium chamber constituting the firstvibration isolating mechanism is in the state open to the open air, thediaphragm provided there freely vibrates. As a result, increase in theliquid pressure in the first liquid chamber is avoided against theentered vibration within the high frequency region, thus reducing thedynamic spring constant of this vibration isolating apparatus as awhole. This isolates vibration within the high frequency region whichcauses a dull sound.

[0040] In the present invention, as described above, the firstequilibrium chamber and the second equilibrium chamber are independentlykept in a negative pressure state or the atmospheric pressure state, ora negative pressure and the atmospheric pressure are alternatelyintroduced at a specific cycle (frequency) into the first equilibriumchamber. As a result, a low dynamic spring constant is available over awide range of frequency regions ranging from low-frequency vibrationmainly comprising idling vibration to high-frequency vibration centeringaround the dull sound. Reduction of the dynamic spring constant thuspermits isolation of idling vibration and vibration associated with thedull sound. Engine shake which is low-frequency vibration can beisolated (inhibited) by obtaining a high damping property.

[0041] In the vibration isolating apparatus of the above constitution ofthe present invention, the housing space is a side branch having aclosed end. Therefore, the vibration isolating apparatus is surelyprovided according to the above constitution.

[0042] Furthermore, the vibration isolating apparatus of the presentinvention in another embodiment comprises a coupler attached to avibrating body; a holder attached to the vehicle body side; an insulatorprovided between the coupler and the holder to absorb vibration from thevibrating body; a vibration isolator having a vibration isolatingmechanism directly following the insulator and comprising a main liquidchamber having a wall thereof formed by a part of the insulator andsealing a liquid therein, an auxiliary liquid chamber connected to themain liquid chamber so as to cause the liquid to flow via an orifice,and an equilibrium chamber provided at a portion of the main liquidchamber via a diaphragm so as to change the volume thereof in thechamber; switching means performing a switching operation based on afrequency required for synchronizing with vibration of the vibratingbody so as to introduce alternately a negative pressure from a negativepressure source and the atmospheric pressure from an atmosphericpressure inlet to the equilibrium chamber; and control means forcontrolling the switching means; wherein: a resistance for slowing downthe introduction of the negative pressure or the atmospheric pressureinto the equilibrium chamber is provided in the middle of acommunicating path communicating between the switching means and theequilibrium chamber.

[0043] In the vibration isolating apparatus of the above configurationof the present invention, the housing space is a side branch having aclosed end.

[0044] In the vibration isolating apparatus of the above configurationof the present invention, the effects substantially the same as those ofthe apparatus of the preceding configuration are available. A resistanceis provided in the middle of a communicating path communicating betweenthe switching means and the equilibrium chamber. The presence of thisresistance slows down the increasing and decreasing rates of thepressure in the equilibrium chamber. Fluctuations of pressure in theequilibrium chamber therefore exhibit a smooth behavior, thus permittingcontrol of fluctuations of the liquid pressure in the main liquidchamber in response to vibration of the vibrating body.

[0045] The liquid-sealing type vibration isolating apparatus of thepresent invention for achieving further another object thereof comprisesan upper coupling member attached to a vibrating body; a lower couplingmember attached to a member or the like on the vehicle body side; aninsulator provided between the upper coupling member and the lowercoupling member to absorb and isolate vibration from the vibrating body;a main chamber having a wall thereof formed by a part of the insulatorand sealing a liquid; an auxiliary chamber connected to the main chambervia a first orifice and having a part of the wall thereof formed by afirst diaphragm; a third liquid chamber connected to the main chambervia a second orifice and formed so as to receive the liquid in the mainchamber; and an equilibrium chamber partitioned and formed by a seconddiaphragm having a higher spring constant than the first diaphragmrelative to the third liquid chamber and receiving any one of theatmospheric pressure and a negative pressure; the liquid-sealingvibration type isolating apparatus further comprises switching means forperforming a switching operation so as to alternately introduce any oneof the negative pressure and the atmospheric pressure into theequilibrium chamber, in synchronization with engine vibration; andcontrol means controlling the switching operation of the switchingmeans.

[0046] By adopting the constitution as described above, the followingfunctions are available in the present invention. As to idlingvibration, a negative pressure and the atmospheric pressure arealternately introduced at a specific frequency into the equilibriumchamber by operating the switching means. More specifically, thepressure (volume) in the equilibrium chamber is altered by operating theswitching means at a specific frequency to absorb fluctuations of theliquid pressure in the insulator and the main chamber caused by idlingvibration entered through the insulator. As a result, there occurs adecrease in the dynamic spring constant of the spring system formed bythe insulator and the vibration isolating mechanism. Particularly in theapparatus of the present invention, operation of the second diaphragmcauses the second orifice having a prescribed volume to connect thethird liquid chamber subjected to pressure fluctuations and the mainchamber, and the liquid in the second orifice resonates withfluctuations of the liquid pressure of the liquid in the main chamberunder the effect of operation of the equilibrium chamber, i.e.,operation of the second diaphragm. Changes in the power generated(vibrating energy) for the entire vibration isolating mechanism are in astate of sine wave not containing high-frequency component noise, andthis ensures absorption and isolation of idling vibration. It is alsopossible to avoid occurrence of high-frequency vibration which mayaccompany the isolation of idling vibration.

[0047] Regarding engine shake which is vibration of a frequency furtherlower than idling vibration, the liquid is caused to flow in the firstorifice connecting the main chamber and the auxiliary chamber, therebyabsorbing and isolating engine shake. More specifically, when vibrationof engine shake is entered (vibration input) into the main chamber, theliquid in the main chamber receives pressure and acts to move the seconddiaphragm downward through the second orifice and the third liquidchamber. However, the second diaphragm forming the equilibrium chamberhas become harder to deform with a higher spring constant than the firstdiaphragm forming part of the auxiliary chamber. Upon input of engineshake into the main chamber, therefore, the liquid in the main chamberflows through the first orifice toward the auxiliary chamber side priorto the deformation of the second diaphragm and to the volume change ofthe equilibrium chamber partitioned and formed by the second diaphragm.A high damping property (high damping force) is available from theflowing motion of the liquid in the first orifice, thereby inhibiting(damping) engine shake.

[0048] In the liquid-sealing type vibration isolating apparatus of thepresent invention as described above, a hardly deformable structure isadopted as a whole for the second diaphragm forming the equilibriumchamber. That is, in the liquid-sealing type vibration isolatingapparatus, the second diaphragm has a constitution having stopper-likeprojections always in contact with both the partition plate forming thelower surface of the equilibrium chamber and the plate partitioning themain chamber and the third liquid chamber, these projections beingarranged on the upper and lower sides near the center of the diaphragm.By adopting the constitution as described above, in the presentinvention, idling vibration is coped with by introducing any one of anegative pressure and the atmospheric pressure at a prescribed cycleinto the equilibrium chamber through operation of the switching means.As a result, the second diaphragm deforms (displaces) under the effectof elastic deformation of the flat portion not containing projections,thereby vibrating the liquid in the third liquid chamber provided abovethe second diaphragm. This causes the vibrating force to propagatethrough the second orifice into the main chamber and acts to inhibit theincrease in the liquid pressure in the main chamber. Reduction of thedynamic spring constant for the entire vibration isolating apparatus isthus accomplished upon input of idling vibration.

[0049] Engine shake is on the other hand coped with by bringing theequilibrium chamber into the state open to the open air throughoperation of the switching means. When engine shake is entered into themain chamber in this state, fluctuations of the liquid pressure in themain chamber are transmitted through the second orifice and the thirdliquid chamber to the second diaphragm in response thereto. Thedeformation region of the second diaphragm itself has however becomenarrower because of the presence of the projections, thus making itharder to deform (displace). The liquid in the main chamber thereforeflows through the first orifice toward the auxiliary chamber having thewall thereof formed by the easily deformable first diaphragm. A highdamping property (high damping force) of the vibration isolatingapparatus is available from this flowing motion of the liquid to thefirst orifice. This high damping force inhibits (damps) the engineshake.

[0050] In the liquid-sealing type vibration isolating apparatus of theconstitution described above, the construction around the seconddiaphragm partitioning the third liquid chamber from the equilibriumchamber comprises a rubber-film-like diaphragm, and a spring serving toalways push back the rubber-film-like diaphragm toward the third liquidchamber. By adopting this constitution in the apparatus of the presentinvention, as in the preceding constitution, against idling vibration,an engine negative pressure and the atmospheric pressure are alternatelyintroduced into the equilibrium chamber by operating the switchingmeans, thereby causing the second diaphragm to deform in the stateresisting to the spring reaction force and eventually preventing theliquid pressure in the main chamber from increasing. As a result, thedynamic spring constant for the vibration isolating apparatus as a wholeis reduced upon input of idling vibration, thus permitting isolation ofidling vibration.

[0051] To cope with engine shake, the pressure transmitted through thesecond orifice and the third liquid chamber to the second diaphragm isreceived with the spring reaction of the spring so as not to causedeformation (displacement) of the second diaphragm. As a result, theliquid in the main chamber flows through the first orifice toward theauxiliary chamber having the wall partially formed by the easilydeformable first diaphragm. A high damping property is available fromthe flowing motion of the liquid in the main chamber into the firstorifice, thus eventually accomplishing damping (inhibition) the engineshake.

[0052] Another liquid-sealing type vibration isolating apparatus of thepresent invention is characterized in that the vibration isolatingmechanism is in a cylindrical shape. More specifically, the apparatuscomprises an inner cylinder forming a coupler attached to a vibratingbody and having a cylindrical shape; an outer cylinder forming a holderattached to the vehicle body side and having a cylindrical shape; aninsulator provided around the inner cylinder between the inner cylinderand the outer cylinder; and a vibration isolating mechanism providedaround the insulator and sealing a liquid which is an incompressiblefluid; the vibration isolating mechanism comprising a main chamberhaving a wall thereof formed by a part of the insulator; an auxiliarychamber connected to the main chamber so as to allow the liquid to flowvia an orifice and separated from the main chamber by a partition platecomprising a rigid body; an equilibrium chamber provided at a part ofthe main chamber via a diaphragm and formed so that the volume thereofin the chamber changes; and an air chamber provided outside theauxiliary chamber via another diaphragm and constantly receiving air;the cylindrical liquid-sealing type vibration isolating apparatusfurther comprising switching means performing a switching operation soas to cause continuous and alternate introduction of any one of anegative pressure and the atmospheric pressure in synchronization withengine vibration, and control means for controlling the switchingoperation of the switching means. By adopting this constitution of thepresent invention, it is possible to achieve further downsizing andreduction of weight, and to save the space for supporting the vibratingbody.

BRIEF DESCRIPTION OF THE DRAWINGS

[0053]FIG. 1 is a sectional view illustrating an engine mount and thelike in accordance with an embodiment of the present invention;

[0054]FIG. 2 is a timing chart illustrating the behavior of a VSV andpressure in an equilibrium chamber with respect to the lapse of time inaccordance with an embodiment of the present invention;

[0055]FIG. 3 is a longitudinal sectional view illustrating a wholeconfiguration of a vibration isolating mechanism in accordance withanother embodiment of the present invention;

[0056]FIG. 4 is a longitudinal sectional view illustrating a wholeconfiguration of a vibration isolating mechanism in accordance withfurther another embodiment of the present invention;

[0057]FIG. 5 is a graph showing changes in dynamic spring constant anddamping coefficient formed by selecting a diameter and a length of anorifice;

[0058]FIG. 6 is a sectional view illustrating a whole constitution of acylindrical liquid-sealing type vibration isolating apparatus inaccordance with another embodiment of the present invention;

[0059]FIG. 7 is a sectional view illustrating an engine mount and thelike in accordance with further another embodiment of the presentinvention;

[0060]FIG. 8 is a timing chart illustrating the behavior or a VSV andpressure in an equilibrium chamber with the lapse of time in accordancewith another embodiment of the present invention;

[0061]FIG. 9 is a partially enlarged sectional view illustrating furtheranother embodiment of the present invention;

[0062]FIG. 10 is a longitudinal sectional view illustrating aliquid-sealing type vibration isolating apparatus in accordance withanother embodiment of the present invention;

[0063]FIG. 11 is a longitudinal sectional view illustrating aliquid-sealing type vibration isolating apparatus in accordance withfurther another embodiment of the present invention;

[0064]FIG. 12 is a partially enlarged sectional view of a pressurecontrol portion provided in the apparatus of FIG. 1; and

[0065]FIG. 13 is a partially enlarged sectional view of a pressurecontrol portion provided in the apparatus of FIG. 7.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0066] Now, an embodiment of the present invention will be describedwith reference to the drawings. An engine as a vibrating body is mountedvia a plurality of engine mounts shown 3 on a vehicle body. The enginemount provided on the rear side is of the liquid-sealing typeconventionally used in general, of which a detailed description istherefore omitted here. The engine mount 3 provided on the front side isof the liquid-sealing type and has a configuration permitting alternateintroduction of a negative pressure and the atmospheric pressure, whichwill be described in detail later.

[0067] The engine has a plurality of combustion chambers (V-type 6cylinders in the present embodiment), and air is sucked and introducedthrough an air cleaner and an air inlet path into each combustionchamber. A throttle valve is provided in the middle of the air inletpath, and the flow rate of sucked air flowing through the air inlet pathis adjusted by opening/closing this throttle valve. A fuel injectingvalve not shown is provided in a port immediately preceding thecombustion chamber of the air inlet path. A combustible mixed gas isformed by a fuel injected from this injecting valve and the aforesaidsucked air and introduced into the combustion chamber. As theconfiguration itself of an engine is conventionally known, a furtherdescription thereof is omitted here.

[0068] Now, the construction of the foregoing engine mount 3 will bedescribed below. As shown in FIG. 1, the engine mount 3 has a coupler 11as a fitting attached to the engine 1, a holder 12 attached to thevehicle body side, an insulator 13 provided between the coupler 11 andthe holder 12 for mainly absorbing vibration transmitted from the engine1, and a vibration isolating mechanism 14 provided immediately followingthe insulator 13. The insulator 13 is made of a vibration-proof rubbermaterial and connected integrally to the coupler 11 by vulcanizationbonding or the like. The vibration isolating mechanism 14 has a wallthereof formed by a part of the insulator 13 and comprises therein amain liquid chamber 15 sealing a liquid therein, an auxiliary liquidchamber 17 connected to the main liquid chamber 15 via an orifice 16 toallow the liquid to flow, an equilibrium chamber 19 provided in aportion of the main liquid chamber 15 via a first diaphragm 18 andformed so as to permit a change in the volume thereof, and an airchamber 21 provided around (under) the auxiliary liquid chamber 17 via asecond diaphragm 20 and always receiving introduced air. The main liquidchamber 15 and the auxiliary liquid chamber 17 are separated by apartition plate 22.

[0069] A communicating path 23 is provided in the equilibrium chamber19, and an end of this communicating path 23 communicates with a vacuumswitching valve (VSV) 31 forming switching means 25 in a pressurecontrol portion as encircled with a dush line in FIG. 1. The VSV 31 is,for example, a three-way valve ON/OFF-switched over by a solenoid 32,and has a first, a second and a third ports 33, 34 and 35. The firstport 33 communicates through the communicating path 23 with theequilibrium chamber 19, as described above. As shown in FIG. 1, thesecond port 34 communicates with the air inlet path in the upstream ofthe throttle valve via an atmospheric pressure duct line 36. The thirdport 35 communicates with the air inlet path in the downstream of thethrottle valve (surge tank) via a negative pressure duct line 37. Avacuum tank as a negative pressure source is provided in the middle ofthe negative pressure duct line 37 to permit constant storage of anegative pressure generated in the downstream of the throttle valve.

[0070] The VSV is controlled by a central processing unit (CPU) 41 ascontrol means. This CPU issues a signal to the effect of ON/OFFswitching over the VSV 31 at intervals of, for example, a predeterminedperiod. When the CPU 41 gives an output of an ON signal, the first port33 and the second port 34 are brought into the communicating state, andsucked air (atmospheric pressure) in the upstream of a throttle valve 7is introduced into the equilibrium chamber 19. When an OFF signal isissued by the CPU 41, on the other hand, the first port 33 and the thirdport 35 are brought in to the communicating state, and sucked air(negative pressure) generated in the downstream of the throttle valve 7and stored in the vacuum tank 38 is introduced into the equilibriumchamber 19. In this embodiment, the vibration isolating apparatus iscomposed of the above-mentioned engine mount 3, the VSV 31 and the CPU41.

[0071] Now, the features of this embodiment will be described. In thisembodiment, a box-shaped expansion chamber 51 having a larger diameterthan that of the atmospheric pressure duct line 36 is provided in themiddle of the duct line 36. The positional relationship of the expansionchamber 51 is important in this embodiment. More specifically, uponintroduction of the open air through the atmospheric pressure duct line36 into the equilibrium chamber 19, pulsation is caused in the suckedair, and the frequency of this pulsation is determined by the length L2of the duct line between the equilibrium chamber 19 and the expansionchamber 51. In this embodiment, the length L2 is set so as to satisfythe following formula:

0.85 c/4f≦L2≦1.15 c/4f

[0072] where, c is the sound velocity (340 m/sec) and f is the requiredfrequency (for example, the one corresponding to the idlingfrequency)[Hz].

[0073] Then, operations and effects of this embodiment having theconfiguration as described above will be described below.

[0074] In the present embodiment, most of the vibration transmitted fromthe engine 1 is absorbed by the insulator 13. Vibration is furthercontrolled and absorbed by the vibration isolating mechanism 14immediately following the insulator 13. That is, the liquid sealed inthe main liquid chamber 15 and the auxiliary chamber 17 flows throughthe orifice 16 as a result of vibration, and the vibration is controlledand absorbed by this flow.

[0075] Along with this, a negative pressure from the vacuum tank and thenegative pressure duct line 37 and the atmospheric pressure from theatmospheric pressure duct line 36 are alternately introduced into theequilibrium chamber 19 provided via the first diaphragm 18 in a portionof the main liquid chamber 15. This introduction is accomplished byswitching of the VSV 31 controlled by the CPU 41 on the basis of therequired frequency (for example, the one corresponding to the idlingfrequency) f. This switching permits alternate introduction of thenegative pressure and the atmospheric pressure at a frequencycorresponding to the required frequency f, and the pressure and hencethe volume of the equilibrium chamber 19 change in response to thisintroduction. Such a change in the volume positively controls andabsorbs fluctuations of the liquid pressure in the main liquid chamber15, produced by the engine 1 vibration and entered through the insulator13.

[0076] Because the VSV 31 is to be changed over by switching, a harmoniccomponent may be produced along with this switching. To avoid thisinconvenience, in this embodiment, the length L2 between the equilibriumchamber 19 and the expansion chamber 51 is set at a value determined bythe foregoing formula. Pulsation is therefore produced in air introducedfrom the atmospheric pressure duct line 36, thus temporarily bringingabout an inertial supercharging state. As shown in FIG. 2, a pressurehigher than the atmospheric pressure would therefore be introduced intothe equilibrium chamber 19. At the same time, a pressure waveform iscorrected, and this would eventually eliminate the unnecessary harmoniccomponent. The pressure in the equilibrium chamber 19 therefore exhibitsa smooth behavior like a sine wave, thus permitting control offluctuations of liquid pressure in the main liquid chamber 15 inagreement with vibration of the engine 1. The driver of the vehicle canconsequently inhibit more certainly the vibration generated from theengine from propagating into the vehicle room.

[0077] According to the present embodiment, the expansion chamber 51 isprovided in the middle of the atmospheric pressure duct line 36.Propagation of vibration into the vehicle room is inhibited by settingthe length L2 between the equilibrium chamber 19 and the expansionchamber 51 at a value satisfying the foregoing formula. The same effectsas those described above are substantially available only byappropriately adjusting the length L2 of the duct line between theexpansion chamber 51 and the equilibrium chamber 19. Therefore, evenwhen an arbitrary length of the atmospheric pressure duct line 36 cannotbe set for piping convenience of the duct line, it is possible toinhibit propagation of vibration without fail.

[0078] In the present embodiment, furthermore, the present invention isapplicable to a case where an engine mounted on a vehicle body is thevibrating body. It is therefore possible to effectively control andabsorb vibration generated by the engine.

[0079] In addition, according to this embodiment, the negative pressuresource should be based on a negative pressure produced in the downstreamof the throttle valve provided in the middle of the air intake path ofthe engine. It is therefore possible to utilize an air intake system ofan ordinary engine, thus eliminating the necessity of a separatenegative pressure source, and permitting inhibition of the increase incost.

[0080] Further, according to this embodiment, the required frequency fis synchronized with the idling vibration. It is therefore possible toeffectively control and absorb the idling vibration of the engine.

[0081] Application of the present invention is not limited to the above,but the details may be modified as follows.

[0082] (1) While the expansion chamber 51 has been provided in themiddle of the atmospheric pressure duct line 36 in the foregoingembodiment, a constitution without an expansion chamber 51 may beadopted. In this case, the length L1 of the duct line between theatmospheric pressure inlet and the equilibrium 19 should take a valuedetermined by the following formula:

0.85 cT/4f≦L2≦1.15 c/4f

[0083] (where, c is the sound velocity [340 m/sec], and T is the periodof time [in seconds] during which the open air is introduced through theVSV 31 into the equilibrium chamber 19), and:

0.85 c/4≦L2≦1.15 c/4f

[0084] And, in this embodiment, as shown in the embodiment of FIG. 7,the communication path 23 may provide with a side branch, and as shownin the embodiment of FIG. 9, the communication path 23 may provide witha resistance portion. Then, the expansion chamber 51 may be usedtogether with the side branch.

[0085] Now, another embodiment of the present invention will bedescribed below. The basic constitution of this embodiment comprises, asshown in FIG. 3, an upper coupling member, i.e., a coupler 11, attachedto a vibrating body, a lower coupling member, i.e., a holder 12,attached to a member or the like on the vehicle body side, an insulator13 provided between the upper coupling member 11 and the lower couplingmember 12 for absorbing and isolating vibration from a vibrating body,liquid chambers 111 and 17 sealing a liquid which is an incompressiblefluid, provided in series with the insulator 13, and a vibrationisolating mechanism 14 formed by an air chamber 21 provided via adiaphragm 20 below these liquid chambers.

[0086] In this basic constitution, the aforesaid vibration isolatingmechanism 14 comprises a main chamber 111 comprising a liquid chamberhaving a wall thereof formed by a part of the foregoing insulator 13,receiving vibration directly from the insulator 13, an auxiliary chamber17 connected to the main chamber 111 via a small-diameter orifice 16 soas to cause the liquid to flow and separated from the main chamber 111with a first partition plate 39, and an equilibrium chamber 19 formedbetween the main chamber 111 and the first partition plate 39 via adiaphragm 18, into which any one of a negative pressure and theatmospheric pressure is introduced. In this constitution, a secondpartition plate 44 serving also as a stopper is provided above adiaphragm 18 forming the equilibrium chamber 19 in the main chamber 111,and further, a second orifice 4 comprising a large-diameter orificehaving a large opening area is provided in a portion of the secondpartition plate 44. In addition, any one of a negative pressure and theatmospheric pressure is continuously or alternately introduced into theequilibrium chamber 19. Switching means 25 conducting switchingoperation so as to alternately introduce the negative pressure and theatmospheric pressure into the equilibrium chamber 19 comprises aswitching valve 31 comprising a three-way valve or the like, and asolenoid 32 for driving the switching valve 31. A throttle valve 29 asshown in FIG. 3 can be provided on the atmospheric pressure introducingport side of the switching valve 31 with a view to balancing theintroducing rate of the atmospheric pressure with the introducing rateof the negative pressure into the equilibrium chamber 19. In thisconstitution, furthermore, control means 41 for controlling operation ofthe solenoid 32 of the switching means 25 is provided in a pressurecontrol portion as encircled with a dush line in FIG. 3. This controlmeans 41 is composed of a microcomputer comprising computing meansmainly including a microprocessor unit (MPU).

[0087] Now, operations of the apparatus in this embodiment will bedescribed below. First, as to idling vibration, a negative pressure andthe atmospheric pressure are alternately introduced at a specificfrequency into the equilibrium chamber 19 provided below the mainchamber 111 by operating the switching means 25. More particularly, thepressure (volume) of the equilibrium chamber 19 is altered byON/OFF-operating the switching means 25, thereby absorbing fluctuationsof the liquid pressure in the main chamber 111 caused by idlingvibration entered via the insulator 13. As a result, the dynamic springconstant of the spring system formed by the insulator 13 and thevibration isolating mechanism is reduced, thus permitting absorption andisolation of the idling vibration.

[0088] As to engine shake which is vibration of a further lowerfrequency than the idling vibration, the liquid is allowed to flowthrough an orifice (small-diameter orifice) connecting the main chamber111 and the auxiliary chamber 17, thereby absorbing and isolating engineshake. Since engine shake vibration has a frequency of about 10 Hz, itis difficult to isolate vibration by reducing the dynamic springconstant. In this embodiment, therefore, a certain negative pressure iscontinuously introduced into the equilibrium chamber 19 forming thevibration isolating mechanism 14 to keep the volume of the equilibriumchamber 19 in null. This causes the liquid to flow through thesmall-diameter orifice 5 formed between the main chamber 111 and theauxiliary chamber 17 to obtain a prescribed damping force by means ofthe viscous drag resulting from this flow of the liquid. The engineshake is damped by this damping force.

[0089] As to vibration of a high frequency within a range of from 100 to600 Hz which causes a dull sound posing a problem during travel of avehicle, the equilibrium chamber 19 is brought into the state open tothe open air by operating the switching means 25, whereby the innervolume of the equilibrium chamber 19 can freely vary relative tovibration of a frequency within the aforesaid range, entered via theliquid in the insulator 13 and the main chamber 111. As a result, theliquid in the main chamber 111 freely flows through the large-diameterorifice 4 of the second partition plate 44 provided in the main chamber111, thus reducing the dynamic spring constant of the spring systemformed by the vibration isolating mechanism. Isolation of high-frequencyvibration is thus accomplished in response to the opening area of theorifice 4. In the apparatus of this embodiment, therefore, a pluralityof kinds of vibration can be absorbed and isolated under the effect ofthe equilibrium chamber 19 having a varying inner volume by operatingthe switching means 25.

[0090] In the apparatus of this embodiment, furthermore, as shown inFIG. 3, a second partition plate 44 comprising a rigid body is providedabove the diaphragm 18 forming the equilibrium chamber 19 in the mainchamber 111. Under the effect of this second partition plate 44,therefore, when an entered vibration from the vibrating body has a largeamplitude, a further downward stroke of the upper coupling member 6brought about by the input of vibration from the vibrating body isarrested at the second partition plate. More specifically, the secondpartition plate 44 serves also as an inner stopper of the vibrationisolating mechanism. Under the effect of this stopper function, thediaphragm 18 forming the equilibrium chamber 19 is protected upon inputof vibration. As a result, the inner volume of the equilibrium chamber19 normally varies, thereby ensuring reduction of the dynamic springconstant.

[0091] In this embodiment, the communication path 23 to the equilibriumchamber 19 may provide with a side branch or a resistance portion, andthe atmospheric pressure duct line 36 may provide with an expansionchamber. Then, the expansion chamber may be used together with the sidebranch.

[0092] Now, further another embodiment of the present invention will bedescribed below with reference to FIGS. 4 and 5. The present embodimentdiffers from that described with reference to FIG. 3 in that threevibration isolating mechanisms are provided, and has a basicconfiguration, as shown in FIG. 4, comprising an upper coupling member11 attached to a vibrating body, a lower coupling member 12 attached toa member or the like on the vehicle body side, an insulator 13 providedbetween the upper coupling member 11 and the lower coupling member 12for absorbing and isolating vibration from the vibrating body, andvibration isolating mechanisms 1, 2 and 3 provided in series with theinsulator 13 and formed by a liquid chamber sealing a liquid which is anincompressible fluid, and the like. In this basic configuration, thepresent embodiment is provided with three vibration isolatingmechanisms. A first vibration isolating mechanism 1 comprises a firstliquid chamber 11 formed below the insulator 13, into which vibrationfrom the vibrating body is entered via the insulator 13, a firstequilibrium chamber 46, formed below the first liquid chamber 11, intowhich a negative pressure and the atmospheric pressure are alternatelyintroduced at a prescribed cycle (frequency), and an elastic film-shapeddiaphragm 45 partitioning the first liquid chamber 11 and the firstequilibrium chamber 46. A second vibration isolating mechanism 2provided below the first vibration isolating mechanism 1 comprises asecond liquid chamber 47 connected to the first liquid chamber 11 of thefirst vibration isolating mechanism 1 via a large-diameter orifice 4, asecond equilibrium chamber 19, provided below the second liquid chamber47, into which a negative pressure or the atmospheric pressure iscontinuously introduced, and a diaphragm 18 partitioning the secondliquid chamber 47 and the second equilibrium chamber 19. A thirdvibration isolating mechanism 3 comprises a third liquid chamber 17connected to the first liquid chamber 11 provided in the first vibrationisolating mechanism 1 via a small-diameter orifice 5, a thirdequilibrium chamber 21, provided below the third liquid chamber 17,comprising an air chamber always receiving the introduced atmosphericpressure, and a film-shaped diaphragm 20 partitioning the third liquidchamber 17 and the third equilibrium chamber (air chamber) 21.

[0093] In this constitution, the individual vibration isolatingmechanisms 1, 2 and 3 are separated by partition members 44 and 39 asshown in FIG. 4, integrally gathered with the insulator 13 and the like,and arranged between the upper coupling member 11 and the lower couplingmember 12 to form a liquid-sealing type vibration isolating apparatus.In this configuration, a negative pressure or the atmospheric pressureis introduced through a first switching means 55 into the firstequilibrium chamber 46 of the first vibration isolating mechanism 1. Inthe pressure control portion as encircled with a dush line in FIG. 4.The first switching means 55 comprises a switching valve 56 comprising athree-way valve or the like and a solenoid 57 operating the switchingvalve 56. The solenoid 57 controls the switching operation by means ofcontrol means 41 comprising a microcomputer mainly consisting ofcomputing means such as a microprocessor unit (MPU). The solenoid 57 isthus driven on the basis of a control signal from the control means 41.An ON/OFF operation of the switching valve 56 maintains the firstequilibrium chamber 46 in any of a certain negative pressure state orthe atmospheric pressure (open to the open air) state, or causesalternate introduction of the negative pressure and the atmosphericpressure at a prescribed cycle (frequency). When the negative pressureand the atmospheric pressure are alternately introduced, a throttlevalve 59 as shown in FIG. 1 is provided on the atmospheric pressureintroducing port side of the switching valve 56 for balancing theintroducing rate of the atmospheric pressure and the introducing rate ofthe negative pressure into the first equilibrium chamber 46.

[0094] A negative pressure or the atmospheric pressure is appropriatelyintroduced through the second switching means 25 at the secondequilibrium chamber 19 of the second vibration isolating mechanism 2.The second switching means 25 comprises a switching valve 31 comprisinga three-way valve or the like and a solenoid 32 for operating theswitching valve 31. The solenoid 32 controls the switching operation bymeans of the control means 41 comprising a microcomputer mainlyconsisting of computing means such as a microprocessor unit (MPU).Therefore, the second switching means 25 performs a switching operationon the basis of the control operation of the control means 41, and thesecond equilibrium chamber 19 is thus kept in a prescribed negativepressure state or the atmospheric pressure state.

[0095] Now, operations of the apparatus in the present embodimentcomprising the constitution as described above will be described below.First, the vibration isolating operation against engine idling vibrationis as follows. Covered frequencies in this case range from about 20 to40 Hz. A negative pressure is therefore introduced through the secondswitching means 25 into the second equilibrium chamber 19 in FIG. 4 tobring the volume of the second equilibrium chamber 19 to null. That is,the operation of the diaphragm 18 in the second vibration isolatingmechanism is prevented. In this state, the negative pressure and theatmospheric pressure are alternately introduced at a prescribed cycle(frequency) into the first equilibrium chamber 46 of the first vibrationisolating mechanism 1. As a result, the liquid in the first liquidchamber 11 provided below the insulator 13 tends to flow toward thethird liquid chamber 17 through the small-diameter orifice 5. However,because the diaphragm 45 forming the first equilibrium chamber 46 isvibrated at a frequency higher than the resonance frequency of theliquid present in the small-diameter orifice 5, and this causesfluctuations of volume of the first equilibrium chamber 46, the liquidin the first liquid chamber 11 cannot flow through the small-diameterorifice. As a result, the liquid pressure in the first liquid chamber 11is caused to largely vary, and the liquid in the first liquid chamber 11vibrates in phase state in which the increase in the liquid pressure inthe first liquid chamber 11 caused by input vibration is canceled. Thedynamic spring constant formed in the first vibration isolatingmechanism 1 and the like is thus reduced.

[0096] As to engine shake which is vibration of a frequency furtherlower than the idling vibration described above, produced during travelof the vehicle, a negative pressure is introduced into the firstequilibrium chamber 46 to bring the volume of the first equilibriumchamber 46 to null. That is, the diaphragm 45 in the first vibrationisolating mechanism 1 is kept inoperable. When vibration is transmittedfrom the vibrating body such as an engine to the upper coupling member11 in this state, the liquid pressure in the first liquid chamber 11increases, and the liquid in the first liquid chamber 11 flows throughthe large-diameter orifice 4 into the second liquid chamber 47 of thesecond vibration isolating mechanism 2. A high damping property isavailable from the flow of the liquid in the first liquid chamber 11through the large-diameter orifice 4. Vibration associated with engineshake having a frequency of about 10 Hz is consequently inhibited. Bymaking the small-diameter orifice 5 capable of coping with vibration ofa lower frequency under 5 Hz than engine shake, it is possible toinhibit such large-amplitude vibration as vibration upon engine crankingwith a low frequency and a large amplitude, and vibration of a largeamplitude produced upon sudden start or sudden acceleration, under theeffect of the small-diameter orifice 5. The small-diameter orifice 5causes the liquid in the first liquid chamber 11 toward the third liquidchamber 17 upon input of an initial load during installation on thevibrating body, to take balance of the inner pressure in these liquidchambers 11 and 17.

[0097] With regard to vibration within a high frequency region of from100 to 600 Hz, which poses a problem of a dull sound in the vehicleroom, the first equilibrium chamber 46 in the first vibration isolatingmechanism in FIG. 4 is brought into the state open to the open air. Atthe same time, a negative pressure is continuously introduced into thesecond equilibrium chamber 19 forming the second vibration isolatingmechanism 2 to bring the second equilibrium chamber 19 into thezero-volume state. The vibration transmitted through the upper couplingmember 6 into the first liquid chamber 11 consequently vibrates theliquid in the first liquid chamber 11. Since the first equilibriumchamber 46 forming the first vibration isolating mechanism 1 is in thestate open to the open air, the diaphragm 45 provided therein can freelyvibrate. As a result, increase in the liquid pressure in the firstliquid chamber 11 can be avoided against the entered vibration of afrequency within the high frequency region, and the dynamic springconstant is reduced for the entire vibration isolating apparatus. It isthus possible to isolate vibration within the high-frequency regionwhich causes a dull sound.

[0098] According to the present embodiment, as described above, it ispossible to obtain a low dynamic constant over a wide range offrequencies ranging from vibration within the low-frequency regionmainly including idling vibration to vibration within the high-frequencyregion covering a dull sound by keeping the first equilibrium chamber 46and the second equilibrium chamber 19 independently in a negativepressure state or in the atmospheric pressure state, or alternatelyintroducing a negative pressure or the atmospheric pressure at aspecific cycle (frequency) into the first equilibrium chamber. By thereduction of the dynamic spring constant, idling vibration and vibrationassociated with dull sound can be isolated. It is also possible toisolate (inhibit) engine shake which is a low-frequency vibration byobtaining a high damping property. The resonance action of the liquidpresent in the orifice 4 and the second liquid chamber 47 and thedynamic spring constant formed at the insulator 13 constituting the mainspring can be caused to agree with a specific target frequency (f₁) asshown in FIG. 5 by bringing the first equilibrium chamber 46 in thisstate into the zero-volume state and appropriately setting the diameterand length of the large-diameter orifice 4. This permits isolation ofvibration having the specific target frequency (f₁).

[0099] In this embodiment, the communication paths to each theequilibrium chambers may provide with a side branch or a resistanceportion, and the atmospheric pressure duct line may provide with anexpansion chamber. Then, the expansion chamber may be used together withthe side branch.

[0100] Another embodiment of the present invention will now be describedbelow with reference to FIG. 6. The basic constitution in thisembodiment comprises, as shown in FIG. 6, an inner cylinder 77 forming acoupler attached to a vibrating body side, an outer cylinder 66, servingas a holder attached to the vehicle body side, to be attached to abracket 12, an insulator 13 provided between the inner cylinder 77 andthe outer cylinder 66 around the inner cylinder 77 connected to thevibrating body, a vibration isolating mechanism 14, provided around theinsulator 13, and formed by a main chamber 15 and an auxiliary chamber17 sealing a liquid which is an incompressible fluid, an equilibriumchamber 19, provided in the main chamber 15 of the vibration isolatingmechanism 14, receiving a negative pressure or the atmospheric pressure,switching means 3 performing a switching operation of the negativepressure or the atmospheric pressure introduced into the equilibriumchamber 19, and control means 41 controlling the switching operation ofthe switching means 25.

[0101] In this basic constitution, the insulator 13 is made of avibration-proof rubber material and integrally bonded to the innercylinder through vulcanization adhering means. The vibration isolatingmechanism 14 comprising the main chamber 15 and the like is providedaround the insulator 13 of this configuration. As shown in FIG. 6, thevibration isolating mechanism 14 basically comprises the main chamber 15following the insulator 13 and having a wall thereof formed by a part ofthe insulator 13, an auxiliary chamber 17 provided opposite to the mainchamber 15 and separated by a ring-shaped partition plate 22, an orifice16 connecting the main chamber 15 and the auxiliary chamber 17 andprovided along the inside of the outer cylinder 66, an air chamber 21provided via another diaphragm 20 outside the auxiliary chamber 17 andconstantly receiving air, and an equilibrium chamber 19 formed via adiaphragm 18 in a space forming the main chamber 15.

[0102] In this basic constitution, the orifice 16 is provided betweenthe main chamber 15 and the auxiliary chamber 17, and the liquid flowsbetween the main chamber 15 and the auxiliary chamber 17. A stoppercomprising a rubber-like elastic body is arranged in the main chamber15, and a rigid protector 88 is provided below the stopper 8. Whenvibration of a large amplitude is entered from the vibrating body, thediaphragm 18 forming the equilibrium chamber 19 is protected by thestopper 8 and the protector 88. The insulator 13 comprising such aconfiguration and the vibration isolating mechanism 14 formed centeringaround the insulator 13 are installed in the outer cylinder 66, and theouter cylinder 66 is attached to a bracket 12 connected to a member orthe like on the vehicle body side.

[0103] In the pressure control portion as encircled with a dush line inFIG. 6, a communicating path 23 is provided at the equilibrium chamber19 forming the vibration isolating mechanism 14 comprising the aboveconfiguration, and an end of this communicating path 23 is connected toa switching valve 31 forming switching means 25. The switching valve 31comprises a three-way valve and causes the equilibrium chamber 19 tocommunicate with a negative pressure source or to the open air byappropriately switching over the vale. The switching operation of theswitching means 25 is accomplished by an integrally provided solenoid32. That is, the switching means 25 is formed by the solenoid valve. Athrottle valve 29 for balancing the introducing rate of the atmosphericpressure and the introducing rate of the negative pressure is providedon the atmospheric pressure introducing port side of the switching valve31 having the configuration described above.

[0104] The control means 41 controlling the switching operation of theswitching means 25 comprises a microcomputer (CPU) formed on the basisof a microprocessor unit. The switching means 25 is driven by thecontrol action of the control means 41 of this configuration, and thiscauses introduction of the negative pressure formed by a negativesuction pressure of the engine or the atmospheric pressure formed byopening to the open air into the equilibrium chamber 19. Introduction ofthe negative pressure or the atmospheric pressure via the switchingmeans 25 drives (deforms) the diaphragm 18 forming a portion of theequilibrium chamber 19, and absorbs fluctuations of the liquid pressuregenerated in the main chamber 15.

[0105] Now, operations of the apparatus of this embodiment having theconstitution described above will be described below. As shown in FIG.6, vibration from the vibrating body side is transmitted via the innercylinder 66 to the insulator 13 comprising a rubber material. As aresult, the insulator 13 vibrates or deforms, thus absorbing orisolating most of the entered vibration. Therefore, most of thevibration is isolated at the insulator 13, while a portion of vibrationis not isolated at the insulator 13, but is isolated at the followingvibration isolating mechanism 14. Now, detailed operations in thevibration isolating mechanism 14 will be described below. First, as toidling vibration, a negative pressure and the atmospheric pressure arealternately introduced at a specific frequency into the equilibriumchamber 19 provided in the main chamber 15 in the lower part thereof byoperating the switching means 25. In other words, the pressure (volume)in the equilibrium chamber 19 is altered by operating the switchingmeans 25 at a specific frequency, thereby absorbing fluctuations of theliquid pressure in the main chamber 15 caused by idling vibrationentered via the insulator 13. As a result, the dynamic spring constantof the spring system formed by the insulator 13 and the vibrationisolating mechanism 14 is reduced, thus accomplishing absorption andisolation of idling vibration.

[0106] As to engine shake which is vibration of a frequency of about 10Hz, lower than that of idling vibration, it is difficult to isolatevibration by reducing the dynamic spring constant. In the presentembodiment, therefore, vibration associated with engine shake isinhibited (damped) by improving damping property in the vibrationisolating mechanism 14. That is, a certain negative pressure isintroduced into the equilibrium chamber 19 forming the vibrationisolating mechanism 14 to bring the volume in the equilibrium chamber 19to null. As a result, the liquid flows through the orifice 16 formedbetween the main chamber 15 and the auxiliary chamber 17, therebyproducing a certain damping force under the effect of viscous dragresulting from the flow of the liquid. This damping force permitsdamping of engine shake.

[0107] Regarding vibration of a high frequency within a range of fromabout 100 to 600 Hz, which causes a dull sound, a problem during travelof the vehicle, on the other hand, the switching means 25 is operated tomaintain the equilibrium chamber 19 in the state open to the open air.The inner volume of the equilibrium chamber 19 can thus freely change inresponse to the vibration of the high frequency entered via the liquidin the insulator 13 and the main chamber 15. As a result, the liquid inthe insulator 13 and the main chamber 15 can freely vibrate, and it ispossible to inhibit the dynamic spring constant of the spring systemformed by the vibration isolating mechanism 14 to a low level, thusimproving the isolating effect relative to high-frequency vibration.

[0108] In further another embodiment of the present invention, thesurface structure at the particular plate forming the equilibriumchamber may be modified (variation). The partition plate has fineirregularities on the surface so as to permit flow of air. These fineirregularities are formed by surface-treating the surface to roughen thesame by the application of shot blasting means or craping means. Asmooth layer is formed by applying a urethane-based paint or asilicone-based paint on the contact side of the diaphragm in contactwith the surface of the partition plate.

[0109] By adopting the constitution mentioned above, when a negativepressure or the atmospheric pressure is introduced, and the vibratingdiaphragm comes into contact with the partition plate, the partitionplate and the diaphragm never come into close contact. Morespecifically, innumerable microspically fine irregularities are providedon the surface of the partition plate in contact with the diaphragm, andcontinuous grooves are formed between these fine irregularities.Therefore, even when the diaphragm is attracted by a negative pressureand comes into contact with the surface of the partition plate havingthese fine irregularities, many gaps are formed between them. Thegrooves formed by these gaps communicate with spaces other than those inwhich the diaphragm is present. The diaphragm therefore never comes intoclose contact with, or is never attracted by, the surface of thepartition plate. As a result, the diaphragm smoothly operates (deforms)in response to introduction of the negative pressure or the atmosphericpressure from the switching means, thus permitting smooth progress ofthe change in the volume of the equilibrium chamber formed by thediaphragm.

[0110] In this embodiment, the atmospheric pressure duct line 51 mayprovide with an expansion chamber, and the communication path 23 mayprovide with a side branch or a resistance portion. Then, the expansionchamber may be used together with the side branch.

[0111] Another embodiment of the present invention shown in FIG. 7 willnow be described below. Because the present embodiment has the samebasic constitution as the embodiment of FIG. 1, only the features asshown in FIG. 13 will be described. In a pressure control portion ofthis embodiment as encircled with a dush line in FIG. 7, a side branch51 constituting a housing space is provided in the middle of thecommunicating path 23 communicating between the first port 33 of the VSV31 of the switching means 25. The side branch 51 is formed in a tubularshape (the diameter should preferably be over 2 mm) so as to branch fromthe communicating path 23 and has a closed tip end. In this embodiment,the length L of the side branch 51 is set so as to satisfy the followingformula:

0.85 c/4′≦L≦1.15 c/4′

[0112] where, c is the sound velocity [340 m/sec] and f′ is thefrequency [Hz] corresponding to the harmonic component in the requiredfrequency (for example, an idling frequency).

[0113] The functions and effects of the embodiment having theconstitution described above will be described. Since the VSV 31 of theswitching means 25 is switched over through switching operation, aharmonic component may result from switching. In this embodiment, incontrast, the side branch 51 is provided in the communicating path 23.Pulsation can therefore be produced in the atmospheric pressure and anegative pressure introduced from an atmospheric pressure duct line 36and a negative pressure duct line 37. As shown in FIG. 8, the resonanceeffect of the pulsation adjusts the pressure waveform, thus resulting inelimination of the unnecessary harmonic component. Presence of the sidebranch slows down the increasing and decreasing rates of pressure in theequilibrium chamber 19. Fluctuations of pressure in the equilibriumchamber 19 therefore exhibit a smooth behavior as a sine wave, therebypermitting control of fluctuations of pressure of the liquid in the mainliquid chamber 15 in response to vibration of the engine 1. As a result,the driver of the vehicle can more certainly inhibit propagation ofvibration from the engine into the vehicle room by means of thevibration isolating apparatus described above.

[0114] According to the present embodiment, it is possible to eliminatethe harmonic component from the produced pulsation by setting a length Lof the side branch 51 so as to satisfy the foregoing formula, thusensuring more certain achievement of the effects described above.

[0115] According to this embodiment, furthermore, the invention isapplicable to a case where an engine 1 mounted on a vehicle body is thevibrating body. It is possible to effectively control and absorbvibration produced in the engine 1.

[0116] In this embodiment, a negative pressure source based on anegative pressure produced in the downstream of a throttle valve 7provided in the middle of an intake path 6 of the engine 1 is employed.It is therefore possible to utilize an ordinary suction system of theengine 1, thus eliminating the necessity of a separate negative pressuresource. As a result, increase in the cost can be inhibited.

[0117] In addition, according to this embodiment, the required frequencyf should be in synchronization with the idling vibration of the engine1. It is therefore possible to effectively control and absorbparticularly idling vibration of the engine 1.

[0118] In this embodiment, as in the embodiment of FIG. 1, theatmospheric pressure duct line 36 may provide with an expansion chamber,and the communication path 23 as in the embodiment of FIG. 9 may providewith a resistant portion. Then, the expansion chamber may be usedtogether with the side branch 51.

[0119] Now, further another embodiment of the present invention will bedescribed below. Because the basic constitution of this embodiment isthe same as that of the above-mentioned embodiment of FIG. 7, the samereference numerals are assigned to the corresponding members and thedescription is omitted here. The following description will thereforecenter around the differences from the second embodiment.

[0120] In this embodiment, as shown in FIG. 9, a foaming body 52 isprovided as a resistance having permeability in the middle of thecommunicating path 23 in place of the foregoing side branch 51.

[0121] This embodiment basically provides the same effects as those ofthe other embodiments shown above. Presence of the foaming body 52provided in the middle of the communicating path 23 communicatingbetween the VSV 31 and the equilibrium chamber 19 slows down theincreasing and decreasing rates of pressure in the equilibrium chamber19. Fluctuations of pressure in the equilibrium chamber 19 exhibits asmoother behavior like a sine wave, thus permitting control of pressurefluctuations of the liquid in the main liquid chamber 15 in response tothe engine 1 vibration, thus ensuring the same effects as those of thepreceding embodiments.

[0122] As further another embodiment of the present invention, avariation shown in FIG. 10 is conceivable in addition to the above. Inthis embodiment, a second diaphragm 18 has stopper-like projections 114and 114′ on the upper and lower sides near the center of the seconddiaphragm 18 with a view to improving the deformation rigidity (springconstant) of the second diaphragm 18. The tip end of the upper one (114)from among the upper and lower projection 114 and 114′ comes intocontact with a partition plate 124 separating the main chamber 15 fromthe third liquid chamber 123. The tip end of the lower one (114′) comesinto contact with a partition plate 39 forming the lower surface of theequilibrium chamber 19 as communicates with a pressure control portionas shown with a dush line.

[0123] As a result, upon introduction of a negative pressure or theatmospheric pressure into the equilibrium chamber 19 through thecommunication path 23 provide with the side branch to cope with idlingvibration, the second diaphragm 18 deforms, i.e., vibrates bydeformation of the projections 114 and 114′, or by deformation(displacement) of the flat portion 112 not having the projections 114and 114′. To cope with engine shake, on the other hand, the stopper-likeprojections 114 and 114′ prevent deformation (displacement) of theentire diaphragm 18, and consequently, the spring constant (deformationrigidity) of the second diaphragm shows a higher value than that of afirst diaphragm 20 provided on the auxiliary chamber 17 side. That is,the liquid in the main chamber 15 flows through the first orifice 16toward the auxiliary chamber 17. As means to improve the deformationrigidity (spring constant) of the second diaphragm 18, there isconceivable a variation of configuration having a spring 115 having aprescribed spring constant, provided below the second diaphragm 18,i.e., on the equilibrium chamber 19 side, and always operating so as topush back the second diaphragm 18 toward the third liquid chamber 123(see FIG. 11).

[0124] In the case of engine shake which is vibration of a frequencylower than that of the above-mentioned idling vibration, the liquid iscaused to flow through the first orifice 16 connecting the main chamber15 and the auxiliary chamber 17, thereby absorbing and isolating engineshake. In this embodiment, more particularly, as shown in FIG. 10, theswitching means 25 is first operated to bring the equilibrium chamber 19into the state open to the open air, thus permitting free vibration ofthe second diaphragm 18 provided at the equilibrium chamber 19. Whenengine shake is entered into the main chamber in this state,fluctuations of pressure of the liquid in the main chamber 15 propagatethrough the second orifice 125 and the third liquid chamber 123 to thesecond diaphragm 18. However, because the second diaphragm 18 has thestopper-like projections 114 and 114′ near the center as shown in FIG.10, and the upper and lower tip ends of these projections 114 and 114′are always in contact with the partition plate 124 between the mainchamber 15 and the third liquid chamber 123 and with the partition plate39 forming the lower surface of the equilibrium chamber 19, it isdifficult for the second diaphragm 18 itself to deform (displace) in thevertical direction. As a result, the liquid in the main chamber 15 flowsthrough the first orifice 16 having a large diameter toward theauxiliary chamber 17 having a wall thereof formed by the easilydeformable first diaphragm 20. A high damping property (a high dampingforce) of this vibration isolating apparatus is available from the flowof the liquid to the first orifice 16, and this high damping forceinhibits (damps) the foregoing engine shake. And, the constitution ofthis embodiment can prevent the generation of such wrong conditions thatthe vibration absorbing characteristic changes due to fatigue of thediaphragm, and the equilibrium chamber is lost due to adhesionphenomenon of the diaphragm to the wall thereof. While, in thisembodiment, the diameter of the second orifice 125 has been set at avalue smaller than the diameter of the first orifice 16, the orifice mayhave a larger diameter, depending upon the degree of rigidity of thesecond diaphragm 18 forming the equilibrium chamber 19. In other words,it suffices that these diameters take values such that, in the stateopen to the open air of the equilibrium chamber 19, the liquid flowspreferentially toward the first orifice 16.

[0125] In this embodiment, the communication path 23 in the pressurecontrol portion as encircled with dush line may provide with aresistance portion, and the atmospheric pressure duct line may providewith an expansion chamber. Then, the expansion chamber may be used withthe side branch.

[0126] Now, another embodiment of the present invention will bedescribed with reference to FIG. 11. This embodiment has the same basicconstitution as the embodiment shown in FIG. 10. It is characterized inthat there is provided a spring 115 serving to push back the seconddiaphragm 18 toward the main chamber 15 on the back of the seconddiaphragm 18. More specifically, as shown in FIG. 11, the vibrationisolating mechanism 14 basically comprises a main chamber 15, providedbelow the insulator 13, sealing a liquid which is an incompressiblefluid, an auxiliary chamber 17 connected to the first chamber 15 via afirst orifice 16 having a large diameter, and partitioned by a softfirst diaphragm 20, an air chamber 21, provided below the auxiliarychamber 17 via the first diaphragm 20, always receiving air, a thirdliquid chamber 123 provided below the first chamber 15 and partitionedby a plate 124, a second orifice 125, provided at the plate partitioningthe third liquid chamber 123 and the main chamber 15, and comprising aplurality of openings, a second diaphragm 18, provided below the thirdliquid chamber 123, and partitioning from the third liquid chamber 123,and an equilibrium chamber 19 partitioned via the second diaphragm fromthe third liquid chamber 123.

[0127] In this basic constitution, the second diaphragm 18 partitioningthe equilibrium chamber 19 and the third liquid chamber 123 is basicallymade of a rubber-film-like member, and has a disk-shaped reinforcingplate 118 for protecting this rubber film, provided on the back (lowerside). The reinforcing plate 118 is formed by a rigid body such as ametallic plate. A spring 115 operating to push back (push up) the seconddiaphragm 18 always toward the third liquid chamber 123 is provided viathe reinforcing plate 118, as shown in FIG. 11, at the reinforcing plate118 of the second diaphragm 18 having the configuration described above.This spring 115 comprises a coil spring in most cases. The coil spring115 is set so as to always push up the second diaphragm and eventuallyensure the volume of the equilibrium chamber 19.

[0128] A plate 124 provided above the equilibrium chamber 19 and thesecond diaphragm 18 partitioning and forming a part of the equilibriumchamber 19 and between the main chamber 15 and the third liquid chamber123 forms a rigid protector. This plate 124 serving also as a protectorprevents the lower end 166 of the upper coupling member 11 from hitting(coming into contact with) the second diaphragm 18 partitioning andforming the third liquid chamber 123 and the equilibrium chamber 19 whenlarge-amplitude vibration is entered into the upper coupling member 11connected to the vibrating body and the insulator 13. That is, the plate124 serves as a down stopper of this vibration isolating apparatus andalso serves to protect the second diaphragm 18. A plurality of openingsare provided at positions off this plate 124 having the aforesaidconstitution, and forms the second orifice for causing the liquid in themain chamber 15 to flow into the third liquid chamber 123 with theseplurality of openings.

[0129] Switching means 25 operating to introduce a negative pressure orthe atmospheric pressure in an appropriately switched state into theequilibrium chamber 19 having the constitution as described abovecomprises a switching valve 31 comprising a three-way valve or the likeand a solenoid 32 driving the switching valve 31, as in the pressurecontrol portion of the embodiment as encircled with a dush line in FIG.11. Control means 41 for controlling a switching operation of thisswitching means 25 comprises a microcomputer (CPU) formed basically bycomputing means such as a microprocessor unit as in the firstembodiment, and detects vibration from a vibrating body such as anengine to control a switching operation of the switching means inresponse to the vibration.

[0130] Now, operations of the apparatus of the embodiment having theconstitution as described above will be described below. Theconstitution is basically the same as that shown in FIG. 10. Thisembodiment is characterized in that, regarding the second diaphragm 18partitioning the third liquid chamber 123 and the equilibrium chamber19, the constitution around the same comprises the rubber-film-likesecond diaphragm 18, and the spring 115 operating so as to push back thesecond diaphragm 18 always toward the third liquid diaphragm 123. Morespecifically, to cope with idling vibration, the switching means 25 isoperated to alternately introduce an engine negative pressure and theatmospheric pressure into the equilibrium chamber 19, thereby causingthe second diaphragm 18 to deform to resist to spring reaction of thespring 115 and vibrating the liquid in the third liquid chamber 123 toeventually cause an increase in the liquid pressure in the main chamber15. As a result, the dynamic spring constant for the entire vibrationisolating apparatus is reduced against idling vibration, thus permittingisolation of the idling vibration.

[0131] To cope with engine shake, fluctuations of liquid pressure in themain chamber 15 is transmitted to the third liquid chamber 123 via thesecond orifice containing the plurality of openings by bringing theequilibrium chamber 19 into the state open to the open air. However,because the second diaphragm 18 provided below the third liquid chamber123 is always pushed up by the spring 115, the second diaphragm 18 doesnot displace (deform) under the effect of this spring reaction(resistance drag) of the spring 115. As a result, the liquid in the mainchamber 15 flows through the first orifice 16 toward the auxiliarychamber 17 having a portion of wall thereof formed by the easilydeformable first diaphragm 20. A high damping property is available fromthis flow of the liquid in the main chamber 15 into the first orifice16, thus permitting eventual damping (inhibition) of engine shake.

[0132] Further, in the pressure control portion the atmospheric pressureduct line may provide with an expansion chamber, and the communicationpath may provide with a side branch or a resistance portion. Then, theexpansion chamber may be used together with the side branch.

What is claimed is:
 1. A liquid-sealing type vibration isolatingapparatus comprising a coupler attached to a vibrating body, a holderattached to a vehicle body side, an insulator which is provided betweensaid coupler and said holder and absorbs and isolates vibration fromsaid vibrating body, and a vibration isolating mechanism which directlyfollows said insulator and is formed with a liquid chamber sealing aliquid which is an incompressible fluid; said vibration isolatingmechanism including a main chamber having a wall thereof formed by apart of the insulator and sealing the liquid, an auxiliary chamberconnected to said main chamber so that said liquid flows through anorifice, an equilibrium chamber which is provided at a part of said mainchamber via a diaphragm and is formed so that the volume thereof in thechamber changes, and an air chamber which surrounds said auxiliarychamber via another diaphragm and constantly receives air; saidapparatus further comprising switching means for performing a switchingoperation so as to alternately introduce any one of a negative pressureand the atmospheric pressure into said equilibrium chamber constantly orin synchronization with engine vibration, and control means forcontrolling the switching operation of said switching means.
 2. Theliquid-sealing type vibration isolating apparatus according to claim 1,wherein said vibration isolating mechanism includes a main chamber whichcomprises a liquid chamber arranged in series with said insulator andhaving a wall thereof formed by a part of said insulator, an auxiliarychamber connected to said main chamber so as to allow said liquid toflow via an orifice to the main chamber and separated by a partitionplate forming of a rigid body from said main chamber, an equilibriumchamber formed via a diaphragm between said main chamber and saidpartition plate and arranged so as to introduce any one of theatmospheric pressure and a negative pressure, and an air chamberprovided under said auxiliary chamber via another diaphragm andconstantly fed with air.
 3. The vibration isolating apparatus accordingto claim 1, further comprising a length L1 of a duct line from saidatmospheric pressure inlet to said equilibrium chamber is set at a valuedetermined by the following formula: 0.85 cT/4≦L1≦1.15 cT/4 where c isthe sound velocity (340 m/sec) and T is a period of time (in seconds)during which the open air is introduced into said equilibrium chamber bysaid switching means.
 4. The vibration isolating apparatus according toclaim 1, further comprising an expansion chamber having a largerdiameter than that of said duct line is provided between saidatmospheric pressure inlet and said switching means, and a length L2between said expansion chamber and said equilibrium chamber is set at avalue determined by the following formula: 0.85 cT/4≦L2≦1.15 cT/4 wherec is the sound velocity (340 m/sec) and T is a period of time (inseconds) during which the open air is introduced into said equilibriumchamber by said switching means.
 5. The vibration isolating apparatusaccording to claim 3, wherein said required frequency is required forsynchronizing with an idling vibration of said engine.
 6. The vibrationisolating apparatus according to claim 4, wherein said requiredfrequency is required for synchronizing with an idling vibration of saidengine.
 7. The liquid-sealing type vibration isolating apparatusaccording to claim 2, wherein said auxiliary chamber is connected tosaid main chamber via a first orifice, separated by a first partitionplate forming of a rigid body and having a part of the wall thereofformed by a first diaphragm, a third liquid chamber is provided to beconnected to said main chamber via a second orifice and formed betweensaid main chamber and said first partition plate so as to receive theliquid in said main chamber; and said equilibrium chamber is partitionedand formed by a second diaphragm relative to said third liquid chamberand receiving any one of the atmospheric pressure and a negativepressure; said liquid-sealing type vibration isolating apparatus furthercomprising a second partition plate serving as a stopper, provided insaid main chamber above said second diaphragm forming said equilibriumchamber; the second orifice provided in a portion of said secondpartition plate.
 8. The liquid-sealing type vibration isolatingapparatus according to claim 7, further comprising a second equilibriumchamber partitioned and formed by a third diaphragm to said secondpartition plate and for continuously introducing any one of a negativepressure and the atmospheric pressure therein in compliance with aswitching operation of the switching means in response to the travelingstate of the vehicle.
 9. The vibration isolating apparatus according toclaim 1, wherein said housing space is a side branch having a closedend.
 10. The vibration isolating apparatus according to claim 7, whereinsaid housing space is a side branch having a closed end.
 11. Thevibration isolating apparatus according to claim 1, wherein a resistancefor slowing down the introduction of the negative pressure or theatmospheric pressure into said equilibrium chamber is provided in themiddle of a communicating path communicating between said switchingmeans and said equilibrium chamber.
 12. The vibration isolatingapparatus according to claim 7, wherein a resistance for slowing downthe introduction of the negative pressure or the atmospheric pressureinto said equilibrium chamber is provided in the middle of acommunicating path communicating between said switching means and saidequilibrium chamber.
 13. The liquid-sealing type vibration isolatingapparatus according to claim 7, wherein said equilibrium chamber ispartitioned and formed by a second diaphragm having a higher deformationrigidity than said first diaphragm relative to said third liquidchamber.
 14. The liquid-sealing type vibration isolating apparatusaccording to claim 13, wherein said second diaphragm has a shape havinga stopper-like projection constantly in contact with the partition plateforming the lower surface of said equilibrium chamber and a platepartitioning between said main chamber and said third liquid chamber, oneach of the upper and the lower sides near the center portion thereof.15. The liquid-sealing type vibration isolating apparatus according toclaim 13, wherein the configuration around said second diaphragmcomprises a rubber-film-like diaphragm, and a spring acting so as toconstantly push back said rubber-film-like diaphragm toward the thirdliquid chamber side communicating with said main chamber.
 16. Theliquid-sealing type vibration isolating apparatus according to claim 1,wherein said coupler is an inner cylinder, said holder is an outercylinder, said insulator is provided around said inner cylinder betweensaid inner cylinder and said outer cylinder; said vibration isolatingmechanism is provided around said insulator, and said air chamber isprovided outside said auxiliary chamber.